[Elecraft] KPA500 PA current

[Jack Brindle]

I have to argue with my friend Jim on this one. The coax itself can be an antenna, and can pick up RF along its path from the antenna to the radio. The best example is a vertical antenna which will use any metal it can find for return currents, which includes the coax after the antenna-mounted choke. This current will combine with the internal shield current at the first place they are connected (which very well may be the SO239 on the back of the ATU). A choke at this point will protect against the problem. This may not be common-mode currents, which is one of the reasons I hesitated in calling it that in my previous email.

Perhaps the best way to make sure there is no current flowing on the outside of coax shield would be to add ferrites along the entire path, a solution that is way to expensive to be practical.

73!
Jack, W6FB

> On Aug 4, 2019, at 10:29 AM, Jim Brown <jim at audiosystemsgroup.com> wrote:
> 
> On 8/4/2019 9:20 AM, Jack Brindle via Elecraft wrote:
>> And, do you have chokes on the coax at the KAT500 or KPA500?
> 
> I hope not -- to be effective, a choke must be that the antenna's feedpoint. A choke on an antenna in the shack does nothing.
> 
> 73, Jim K9YC
> 
> 
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